Manufacture of photographic emulsions



July 2, 1946.

T. T. BAKER MANUFACTURE OF PHOTOGRAPHIC EMULSIONS Filed May 31, 1945.

4 5413 Asa/eds INV'eNTbI? Patented July I h UNITED STATES PATENT OFFICE MANUFACTURE OF PHOTOGRAPHIG EMULSIONS Thomas Thorne Baker, Pinner, England Application May 31, 1945, Serial No. 596,918 I In Great Britain May 30, 1944.

10 Claims. (01. 95-1 (Granted under the provisions of sec. 14, act of 1 March 2, 1927; 357 0. G. 2 This invention is for improvements in or reuse of alcohol or other liquid .dehydrating agents lating to the manufacture of photographic emuland enabling the drying operation to be carried sionsand has particular reference to the prepaout by heating. ration of an emulsion by a method which involves I have found that drying of granules of emulthe removal of a considerable part of its water 5 sion by heating can be carried out without risk so that it can be handled and stored in a more of the granules agglomerating, amalgamating or less dry state in the form of small granules or sticking if, prior to the application of heat, or grains. r the surfaces of the granules are subjected to a It has been shown by Carroll 8; Hubbard in hardening treatment. Communication No. 340 of the Bureau of Stand- 10 According to the present invention, there is ards, U. S. A. (and reprinted in Bureau of standprovided a method of preparing a photographic ards, Journal of Research, vol. 'lgAugust, 1931) gelatin emulsion which is semi-dried, as hereinthat an emulsion if not finished," 1. e. not maalter defined, which method comprises shredtured, to completion will go on maturing in the ding a partially stabilized silver halide gelatin dry state and so alter in its photographic charemulsion treating the granules thus formed with acteristics, and it is an inherent part of the presa solution of sodium sulphate to harden the surent invention that the part-maturation of-the faces of thegranules and thereafter drying the emulsion during its manufacture plus the extra granules at a temperature not substantially maturing to which it is subjected in drying reabove 90" F. to form a freely-flowing granular suits in an optimum overall maturation, thus mass.v

providing a well-stabilized product. In other L The term "semi-dried as applied in this speciwords, the heat applied in the drying which confication to a gelatin emulsion means an emulsion stitutes one of the steps of the present invention containing 4 to 16% moisture. It is known that, is designed to complete the digestion or maturaair-dried leaf gelatin may contain about 16.5% tion or finishing of the emulsion and to stabilize moisture and after drying over sulphuric acid for it so that if kept for long periods even in hot 8- year the mo ure n t m S l be about climates its photographic characteristics on be- 2%. Drying to amoisture content substantially ing used for sensitizing purposes ar not apprelower than 4% produces a gelatin which has inciably changed. Sensitometric tests carried out r a a edu ed pow of a es upo being over a long period confirm that the emulsion reconstituted.

made in accordance with the present invention -By treatment with sodium sulphate soluti does not alter appreciably in photographic charpreferably a concentrated solution, e. g. one acteristics on long keeping. which is substantially saturated the surface or In United States Application Ser. No. 493,922. pidermis ofe ch in iv ual ranule f he flledJuly 8, 1943,'I have described a method of shredded emulsion is hardened so that heat can pr p ring a partially but not completely digested be applied, prefer bly in the form of warm dry gelatino-silver-halideemulsion and after. washair at a temperatureof between 85 F. and not ing the emulsion in the known manner to shred su t n i y above 9 F. and having a r tive the jelly through a shredder plate with standard humidity of 25 to to O t n h g nul s 1' size perforations and then to re-shred these 40 h dried emulsioninthe freely flowing formshreds through line nickel or silver or other in- Sodium sulphate is known to prevent the swellnocuous gauze of a mesh of about 30 per inch ing of gelatin in the presence of water, and I so as to mince them into tiny granules of jelly, have found that the presence in a solution of this The minced granules are. then dried with the substance of an alum, e. g. potash alum in a aid of heat. but in so doing the granules are apt minor proportion, e. g., 0.02 to 2.5% and preferto agglomerate, amalgamate or stick together'in ably 1 to 2.5% by weight of the weight of the lumps, whereas it is very important from the sodium sulphate hardens the rface l rs 0! point of view of obtaining a product'which is the granules and thus prevents agglomeration.

readily handled and used that the granules One example of a' solution containing sodium should remain discrete and well separated so that sulphate and potash alum for use in accordance the material will pour more or less like coarse with the present invention consists of-water 200 sand. litres, sodium sulphate 4 0 kilograms, potash alum One method of desiccation designed to mini- 1 kilogram. The amount of potash alum must niise or obviate the disadvantage above-referred not be unduly in r as d the wise there is dullto involves .the treatment of the granules with a culty in reconstituting the emulsion and the dehydrating liquid such as methyl or ethyl alccv actual proport n of P h m Will d p nd hol or acetone. inter alia. on the character of thegelatin and of It is an object of the present invention to prothe water. vide a method of preparing granular gelatino-' The. granules of gelatin emulsion are prefersilver-halide photographic emulsion avoiding the on ably dropped into the sodium sulphate solution allowed to remain for example for a time of the halide emulsion.

- at least one-half.

' 8nd by order of 20 minutes and are then drained free from liquid and washed once or twice with ice- ;eold water to wash away most of the excess of sodium sulphate. The well-drained granules are.

then spread on nickel, silver, stainless steel or a other trays of gauze of a metal innocuous to the =emulsion or put into a rotating gauze drum of i such metal and subjected to treatment with warm air, e. g. at a' temperature between 85 and 95 F. -or at a somewhat higher temperature should this be indicated by preliminary experiment to be necessary to complete the mature ltion or finishing of the emulsion. The drying- :operation may take, for example, about 12 hours. a The invention may be applied with particular advantage to the treatment of a partially-digested silver halide emulsion, completion of the digestion or maturation of the emulsion being 20 eflected during the drying stage. Alternatively,

. but less desirably, the invention may be carried into effect upon a fully digested or finished silver In carrying out the present invention, emulsions of a far more concentrated'type than those normally employed may be used. Thus, a processed emulsion containing when finished 50 grams of silver bromide and 80 grams of gelatin Per litre which would in the first stage be madeup to about one-half litre only, owing-to the swelling during-washing, may in accordance with the present invention be so highly concentrated that its volume prior to washing would be of the }order of one-quarter litre and about one-half litre after washing. It will be understood that theprocess of semi-drying is thus cut down by Following is a description by way of example and with reference to the accompanying diagrammatic drawing of one method of carrying the invention into efiect.

i In the drawing: .1

Figure 1 shows (a) the first shredding step in preparing the granules of emulsion; (b) the sec- .ond shredding .step and treatment of the granules in sodium sulphate solution; washing Figure 2-shows an alternative form of drying apparatus.

. Referring to Figure 1- inwhich similar reference numerals denote similar parts, II is the chamber of a shredding press whichis provided with piston I! for forcing the set gelatin emul-- sio'n It or the shredded gelatin emulsion ll through the shredder plate II or the gauze of innocuousmetal It. The shredded emulsion ll iscollected in a receptacle ll. Thedoublyshredded emulsion II is dropped into a solution ll of sodium sulphate containing potash alum in a vessel 20 provided with a stirrer II.

Draining of the shredded and washed emulsion 22 is carriedout ina funnel 23, the granules being supported by a piece ofrabric ll. Suction is apgl'ied to the granules by way er fiber- Ill-Figure -1 granules Ila-re sup -ported'inagauzetray'll whichisplacedina drying chamber-20. Warm"air is passed over betweenthegranulesinthedirectionshcwn- In the alternative drying apparatus shown in Figure-2, the drained granules are placed in a anuse'dnnnil mo'tmtedinadrylngchamberil.

through which warm air is passed in the direction of the arrows. The drum is mounted on Grams A. Water 200 Ammonium bromide 16 m Ammonium iodide 0.5 Gelatin 6.0

(Used at 100 F.)

B; Silver nitrate 25 Water Ammonia, suflicient in amount Just to redissolve the precipitate at first formed.

(Used at 65F.) 0. Silver nitrate Water 90 1 (Used at 110 F.)

Solution 3 is added to solution A with rapid stirring and after being allowed to stand for '5 minutes solution C is added with rapid stirring. At once thereafter 104 grams of dry gelatin are add- 25 ed and dissolved, the mixture.poured into an ice-cold Jar and allowed to stand in ice water withstirring until gelling commences. V v

Next day, the set emulsion is shredded by passing it through a perforated plate of innocuous metal and the shreds or noodlesare washed for minutes with 3 minute changes of water or until the pH of the last wash water is pH 8 orslightly under.

The washed emulsion is then re-melted, the 85 temperature raised to 120 F. and after the addition of 5 grams of a. 2% solution of glacial acetic 7 acid is digested at that temperature for 40 minutes. It is then set and the set Jelly conveniently at a. temperature of about 40 F. is shredded first through a standard shredding press and then through wire gauze (about 30 meshes per linear inch) made of a metal innocuous to the emulsion, the very small granules after the second shredding being dropped into a sodium sulphate potash alum solution .consistingof sodium sulphate 850 grams, 5% aqueous solution of potash alum 18 cc. and water 4,000 cc. y The granules are allowed to stand in contact with this solution for about 20 minutes and are 0 then removed, drained e. g. by suction, washed with one or two applications of ice-cold water a current of warm air having a relative humidity 0125 to and a temperature of between 85 and F. or a little over. 4 g The drying operation may be carried out in a rotating gauze drum of innocuous metal (as indicated in Figure 2) or in trays of gauze which are arranged in a drying chamber provided with means for introducing the .warm air and for leading away the ai -after it has swept through and overthes nulesiseerigurei). I

1. A method ofpreparing a photographic gelatin emulsionin theiform of apparently dry and freely-flowing granules which method comprises shredding a silver halide gelatin emulsion, treat-' in: the granules thus formed witha concentrated solution .of sodium sulphate of dehydrating strength to harden the surfaces of the granules and thereafter drying the granules at a temperature of about 851 to F. until: the moisture.

content of said granules is' reduced to 4 to 14%. 75-.2.Amethodofpreparlngamatured photomethod comprises shredding a partially digested silver halide gelatin emulsion into granules,

treating the granules with a substantially saturated solution of sodium sulphate containinga minor proportion of an alum to harden the surfaces of the granules separating the granules from the liquid and thereafter heating the granules in warm air at a temperature of about 85 to 95 F. until the moisture content of said granules is reduced to 4 to 14% to complete the maturation of the emulsion and to bring the granules to the apparently dry and freelyflowing condition. a

3. A method of preparing a photographic gelatin emulsion in the form of apparently dry and .freely-flowinggranules which method comprises shredding a fully digested-silver halide gelatin emulsion into granules, treating the granules with a substantially saturated aqueous solution of sodium sulphate containing a minor proportion of an alum, separating the granules from the liquid and thereafter heating the granules in warm air at a temperature of about 85 to'95 F.

until the moisture content of said granules is reduced to 4 to 14%, and until the granules attain the apparently dry and freely flowing condition. g

4. A method of preparing a matured photographic gelatin emulsion in the form of apparently dry and freely flowing granules which method comprises forming a partially matured from the liquid and subjecting them to drying at a temperature of about85 to about 95 F. in a current -of air until the moisture content of said granules is reduced to 4 to 14% and the granules are apparently dry and freely flowing and until the emulsion is substantially completely matured.

5. A method of preparing amatured photographic gelatin emulsion in the form of apparently dry and freely-flowing granules which method vcomprises forming a partially matured silver halide photographic gelatin emulsion into tion of sodium sulphate containing .a minor proportion of potash alum for a time sufficient to effect hardening of the surface layers of the granules but insuflicient to affect substantially the subsequent reconstitution of the emulsion,

separating the granules from the liquid and sub- Jecting them to drying at a temperature of about 85 to 95 F. in a current of warm air having a relative humidity of 25 to until the moisture granules by double shredding, immersing the said granules for a time of the order of 20 minutes in a concentrated aqueous solution of sodium sulphate of dehydrating strength containing a minor proportion of potash alum, separating the a I granules from the liquid and subjecting them to drying at a temperature from 85 to 90 F. in a current of air until the moisture content of said granules is reduced to 4 to 14% and the granules are apparently dry and freely flowing and until the emulsion is substantially completely matured.

8. A method of preparing a matured photographic gelatin emulsion in the form of appargranules by double shredding, immersing the granules in a concentrated aqueous solution of sodium sulphate of dehydrating strength congranules by. double shredding, immersing the said granules in a substantially saturated solution of sodium sulphate containing a minor proportion of potash alum for'a time sufllcient-to effect hardening of the surface layers ofv the granules but insuillcient to affect substantially the subsequent reconstitution of the emulsion, separating the granules from the liquid and subjecting them to drying at a temperature of about85 to 95 F. in a current of air until the moisture content of said granules is reduced to 4 to 14% and the granules are apparently dry and freely flowing and until the emulsionis substantially completely matured.

6. A method of preparing a matured photographic gelatin emulsion in the form of apparently dry and freely-flowing granules which method comprises forming a partially matured silver halide pho osmphic'gelatin emulsion into granules by double shredding, immersing the said granules in a substantially saturated solutaining potash alum in amount'equal to 1% to 2.5% by weight of the weight of sodium sulphate,

separat ng the granules from the liquid andsubje'cting them to drying at a temperature from about 85 to about 95 F. in a current of air until the moisture content of said granules is reduced to 4 to 14% and the granules are apparently dry and freely-flowing and until the emulsion is substantially completely matured.

9. A method of preparing a matured photographic gelatin emulsion in the form of apparently dry and freely-flowing granules which method comprises forming a partially matured silver halide photographic. gelatin emulsion into granules by shredding through a. perforated plate and then through a wire gauze of innocuous metal, treating the granules with a substantially rent of air until the moisture content of said granules is reduced to 4 to 14% and the granules are apparently dry and freely flowing and until the emulsion is substantially completeLv matured.

10. A stabilized silver halide photographic gelatin emulsion in the form of freely-flowing non agglomerating surface-hardened granules having a moisture content between 4 and 14% and capable of being freelyreconstituted to the gel state and obtained by the process set forth in v claim 4.

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